Determination of the glass transition temperature in thin polymeric films used for microelectronic packaging by temperature-dependent spectroscopic ellipsometry

We characterized the glass transition temperature T-g of thin polyimide films by temperature-dependent spectroscopic ellipsometry and compared the results to DSC measurements of the bulk polymer. The effect of the curing temperature on T-g and the thermal expansion alpha(T) was analyzed. An improved ellipsometric data evaluation was used to get most precise and reliable T-g data. T-g increased with increasing curing temperature, while the bulk T-g was considerably lower than the thin film T-g. Both observations are attributed to the temperature sensitive release of the imidization by-product 2-hydroxyethyl methacrylate (HEMA) and crosslinker components as well as decomposition products from the material. Variation in the curing temperatures of 230-380 degrees C led to an increase in the T-g of 34 degrees C. (C) 2017 Elsevier Ltd. All rights reserved.